Interpretation
| Result | Meaning |
|---|---|
| ≥ 80% predicted/personal best | Green zone |
| 50–79% | Yellow zone: caution |
| < 50% | Red zone: medical alert |
Formula
Men: ln PEF = 0.544 ln(age) − 0.0151 age − 74.7/height(cm) + 5.48. Women: ln PEF = 0.376 ln(age) − 0.0120 age − 58.8/height(cm) + 5.63 (Wright scale, L/min). EU scale = 50.356 + 0.4W + 0.0008814W² − 0.0000001116W³. Children < 15: height-based EU-scale table, linear interpolation.
Clinical pearls
- A patient's own personal best is a better reference than population predictions for asthma action plans.
- Modern meters use the EU/EN 13826 scale, which reads lower than the old Wright scale in the mid-range; compare readings against the same scale.
- Reference values come from white European non-smokers; normal readings in men can be up to 100 L/min (women 85 L/min) below predicted.
Examples
predicted peak flow 40 yo male 175 cmpeak flow 35F 165 cm measured 300expected pef for a 10 year old 130 cm tall
FAQ
What is a normal peak flow for a 40-year-old man?
About 630 L/min (EU scale) for a 175 cm 40-year-old man; readings within about 100 L/min of predicted are normal.
What are peak flow zones?
Green is ≥ 80% of personal best or predicted, yellow 50–79%, and red < 50%, which needs urgent treatment.